Biofuel containing furanic compounds and alkoxy benzene compounds and the process for obtaining these compounds from sugar cane by hydrolysis of  cellulose, sugars and lignin in ionic liquids

ABSTRACT

A biofuel consisting of a mixture of furanic compounds and polymethoxy benzene compounds which can be mixed with standard fuel consisting in hydrocarbons, and the process to obtain these compounds from sugar cane by converting cellulose, hemicellulose and sugars in furan derivatives and levullinic acid esthers and by converting lignin in alkoxy benzene compounds by hydrolysing the cellulose and lignin of sugar cane first in a mixture of N alkyl imidazolium chloride, hydrochloric acid 37% and an alcohol, dehydrating pentoses and hexoses so obtained from cellulose, stabilising the aldehyde groups as acetal and stabilising the phenolic hydroxyls obtained from lignin as alkyl ethers.

1. FIELD OF INVENTION

Liquid biofuels from cellulose and lignin, ionic liquids, renewable energy, solvent extraction from ionic liquids

2 . BACKGROUND OF THE INVENTION

The world production of cellulose and lignin on land is 60 billion ton per year and the stock of cellulose and lignin is 1 000 billion ton.

The world consumption of fossil fuels is 8 billion ton per year.

The food production in the world is 3 billion ton per year.

From these 3 numbers we conclude that, to take out from food, materials to produce bio ethanol or vegetable oils for biodiesel would not solve the problem of substituting fossil fuels, and would cause hunger.

On the other side, there are large surfaces of arable land, which are not cultivated or which produce plants not suitable for food. In these surfaces, the production of cellulose and lignin from trees or bush is possible. On the other side, cellulose and lignin contained in biomass is a side product of many food crops.

One of the crops which produce large quantities of cellulose and lignin per hectar and per year is sugar cane, which has an yield of 80 ton per hectar.

In one ton of sugar cane there are about 80 kg of sugar, which may be converted to 40 kg of bioethanol. Besides sugar there are 250 kg of cellulose and hemicellulose and 120 kg of lignin, which is presently not converted to liquid fuels.

The substitution of fossil fuels is also an important motivation to improve the process for producing biofuels, because of the carbon dioxide which they produce by burning. Although cellulose and lignin also produce carbon dioxide by burning, the same quantity of carbon dioxide was previously taken out of the atmosphere by photosynthesis to produce cellulose and lignin.

As a consequence, to convert cellulose and lignin into a liquid fuel is since decades a challenge for scientists, because the existing cars and trucks could drive with such a liquid biofuel without major changes in the motor.

The exhausting oil reserves and the political dependence on unstable countries producing oil is also a major problem today, which motivates the research of renewable alternatives.

3. DETAILED DESCRIPTION OF THE INVENTION

In our patent U.S. Pat. No. 8,247,581 and patent application U.S. patent Ser. No. 13/371,410 we described a process where cellulose hydrolyses to glucose in a solvent consisting of N-Alkyl imidazolium chloride (NAIC) mixed with a small quantity of hydrochloric acid and an alcohol. In this reaction medium glucose opens the pyran ring, the carbonyl function moves from position 1 to position 2, the ring is closed to a furan ring or partially remains open. The carbonyl group is stabilised as an acetal.

Although the use of an acetal to protect a carbonyl function is well known for those skilled in the art, the application of the acetal to this particular reaction conditions is not at all evident, as we are using an ionic liquid, the pH is under 3, and the conclusion that the carbonyl groups of glucose are stabilised by the acetal is also not evident.

In a second step we eliminate the water and the alcohol from the reaction mixture and add a small quantity of hydrochloric acid to catalyse the dehydration.

In a third step we add an alcohol again and heat to 60-90° C. in order to produce the acetal of HMF, the esther of levullinic acid and the alkoxy benzenes drived from the polyphenols existing in lignin.

In a fourth step we extracted from the NMIC mixture the acetal of HMF, the esther of levullinic acid and the alkoxy phenols with a cetone. The cetone extract was washed with water in order to further eliminate chloride ions.

After evaporation under vacuum of the solvent, we made GC-MS to identify the product.

We now found that using sugar cane directly instead of cellulose, as we made previously, there were 2 important improvements:

-   -   The cellulose contained in sugar cane had a crystallinity more         favourable to hydrolysis than the cellulose which we used in         previous trials, which was supplied from the cellulose and paper         industry.     -   Lignin was also hydrolysed under the reaction conditions,         producing alkoxy benzenes.

These finding are very important, because in this way we converted about 45% of the sugar cane in biofuel.

Considering that 55% of sugar cane was water, this conversion is excellent and does not need any recycling of unreacted sugar cane.

We further found that after one month using the ionic liquid in a continuous process, it is easy to purify it from accumulating side products, just by neutralising the mixture with sodium hydroxide, falling out the sodium chloride an filtering.

N-methyl imidazole is obtained by vacuum distillation.

The ionic liquid in case o N-methyl imidazolium chloride is obtained according to U.S. Pat. No. 4,450,270 to BASF from inexpensive raw materials.

EXAMPLE

In a round bottom flask we stirred under reflux at 60° C.:

NAIC 100 g Sugar cane  40 g Hydrochloric acid 37%  30 g 1-Pentanol 100 g

After 2 hours, we took a sample of 20 ml of the reaction mixture, we added 20 ml of water to fall out any solids from sugar cane which did not react. We found that 95% of sugar cane reacted.

We distilled under vacuum the water and pentanol from the reaction mixture. We added to the concentrate:

Hydrochloric acid 37% 10 g and heated at 110° C. After one hour, we added 30 g pentanol and heated to 110° C. during 2 hours to stabilise as acetal or respectively phenolic ethers.

We made 3 extractions with 100 g hexanone each extraction.

The hexanone extract was washed 2 times with:

Water 30 g

The hexanone extract was evaporated.

We made GC-MC of the residue and found:

-   -   Acetal of HMF     -   Alkyl esther of levullinic acid     -   3 main alkoxy benzenes         corresponding to 90% of the stechiometric conversion.

The mixture of these compounds has a boiling range of 150-200° C., just between gasoline and diesel oil. 

1. A product suitable to use as a biofuel consisting of a mixture of the acetal of hydroxymethyl furaldehyde, levullinic esther, alkoxy benzenes, which can be mixed with both gasoline and diesel oil for motor cars and a process for obtaining this biofuel consisting in solving sugar cane or a similar crop containing cellulose, hemicellulose, sugar and lignin in a mixture of N-alkyl imidazolium chloride (NAIC), hydrochloric acid 37% and an alcohol, hydrolysing cellulose into the acetal of glucose, hydrolysing the lignin in phenolic compounds, evaporating the alcohol and water, dehydrating the glucose acetal to the acetal of hydroxymethyl furfural, adding to the reaction mixture an alcohol to produce the acetal of HMF, the esther of levullinic acid and the alkoxy benzenes, extracting the reaction products from the ionic liquid phase, taking out the residues of the ionic liquid from the organic phase by extracting the ketone extract with water, evaporating the ketone extract to isolate the reaction products.
 2. The process of claim 1 where the reaction mixture for hydrolysing cellulose is a mixture containing 20-80% of an ionic liquid composed of N-alkyl imidazolium chloride with the alkyl group with 1 to 10 carbon atoms, containing also 2-15% of hydrochloric acid 37%, and containing an alcohol, which may contain carbon atoms C1-C6 in a quantity that makes the sum of the components of the reaction mixture 100%.
 3. The process of claim 1 where the temperature of the hydrolysis reaction is 50-120° C., the temperature of the dehydration reaction is 60-100° C. and the temperature to produce the acetal, the esther and the phenolic ether is 80-120° C.
 4. The process of claim 1 where the first extraction is made with a ketone in C5 to C10 in a quantity which may vary between 10 and 50% of the NAIC phase.
 5. The process of claim 1 where the second extraction is made with water in order to remove the residues of the ionic liquid from the keton phase.
 6. The process of claim 1 where the extract free from ionic liquid is evaporated in vacuum to obtain a mixture suitable as a component for standard fuel for motor cars, in a proportion of 5% to 50% in weight of biofuel to hydrocarbons.
 7. The process of claim 1 where the conversion of sugar cane in acetal of hydroxymethyl furaldehyde, esther of levullinic acid, alkyl ethers of benzene is 95%
 8. The process of claim 1 where reactions can be made in batch or continuously
 9. The process of claim 1 where the ionic liquid can be recovered after one month recycling by neutralizing the hydrochloric acid with sodium hydroxide and distilling the N-Methyl imidazole. 